A conventional power converter device has a power module that includes power semiconductors and converts between DC power and AC power by a switching operation of the power semiconductors. The power module further includes a base plate for heat dissipation, on which the power semiconductors are arranged. Heat generated by the power semiconductors is released to the base plate described earlier through a main surface on one side of the power semiconductors. On the base plate described earlier, in addition, fins are formed on a surface of the other side of the side where the power semiconductors are arranged, and a cooling medium contacts directly with the fins.
This kind of a power converter device is disclosed in Patent Reference Literature 1 for instance.
However, further improvement in cooling performance requires expansion in the heat dissipation area of the power semiconductors. Expansion in the heat dissipation area of the power semiconductors causes the power module structure to become complicated and leads to reduced productivity of the power module, thereby becoming a factor of cost rise of the power converter device.    [Patent Reference Literature 1] Japanese Laid-Open Patent Publication No. 2008-29117